Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations exist, so the description carries the full burden, and it does disclose the operationally critical traits: passive reconnaissance, no packets sent to the target, and the exact upstream sources with fallback behavior. What is missing is output shape (flat hostname list? deduplicated? sorted?) and whether upstream rate limits can delay results.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Dense but front-loaded: the enumeration action and source come first, then the passivity guarantee, then the use cases. Each clause adds information and nothing is redundant with the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter, no-output-schema tool the description covers source, safety profile, and intent, so an agent can decide and call it correctly. It only lacks expected return shape and any bounds or rate-limit caveats on the upstream CT sources.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Only one parameter and schema coverage is 100%, so the schema already documents the domain format. The description adds no syntax, validation, or edge-case detail (e.g. wildcard handling, subdomain-only input, IDN support) beyond what the schema states, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Specific verb (enumerate) plus resource (a domain's subdomains) with the data source named (Certificate Transparency logs, crt.sh with Cert Spotter fallback). This clearly separates it from siblings like ssl_cert_check, whois_lookup, or dns_propagation_check, which touch adjacent data but do not enumerate hostnames from CT logs.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives concrete use cases (attack-surface reviews, migration inventories, hunting forgotten test/staging hosts), which tells the agent when this tool is the right pick. It stops short of explicit when-not conditions or naming an alternative sibling, so it is context rather than routing guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.